1. Field of the Invention
This invention relates to a semiconductor treatment apparatus, and more particularly to a treatment apparatus for supplying a process chamber with a process gas formed of a mixture of a carrier gas and a raw material gas.
2. Description of the Related Art
In semiconductor treatment apparatuses such as a thermal treatment apparatus, a diffusion apparatus, and a CVD apparatus, a process gas formed of a mixture of a carrier gas and a raw material gas is supplied into a process chamber to treat a semiconductor wafer or an LCD substrate. In the case of the CVD apparatus, for example, a silicon-base compound such as tetraethylorthosilicate (TEOS), or an organic metal compound such as triisobutylauminium are used as the raw material gas in many cases.
The raw material gas is reserved in a reservoir generally in the form of liquid as a raw material liquid. The raw material liquid is bubbled with the use of the carrier gas to be vaporized. The reservoir is located in a constant-temperature bath. The process gas formed of a mixture thus obtained is transferred through a supply line into a process chamber. The flow of the process gas is controlled by a mass flow controller while it is transferred therethrough. To prevent a raw material gas from being liquefied during the transfer, the supply line is covered with a heating member such as a heating tape.
The mass flow controller has a bypass pipe branching from a main pipe connected to the supply line. Part of the process gas flowing through the bypass line is heated, and the flow of the entire gas mixture is measured on the basis of the movement of heat. However, the bypass pipe has a very small inner diameter, for example, of 1 mm or less, and hence can easily be choked while such a gas is passed therethrough. Therefore, measuring errors are apt to occur and the flow control of the process gas cannot be performed with accuracy.
It is considered that the bypass pipe is choked with by-products resulting from liquefaction of the raw material gas or decomposition of the raw material gas heated in the pipe.